1. Field of the Invention
The present invention relates to a pulley unit provided at auxiliary machines driven via a belt by a crank shaft of engine for automobile, including a compressor for air conditioner, a water pump, an alternator, and a cooling fan.
2. Description of the Related Art
Various types of auxiliary machines provided at an automobile engine are driven via a belt by a crank shaft of the engine. For example, assuming that an alternator is coupled so as to rotate synchronously with a crank shaft of an engine, if the rotational speed of the crank shaft is decreased, a power generating efficiency of the alternator is also decreased. Then, a pulley unit has been devised that a one-way clutch is built in a pulley portion of the alternator, when the rotational speed of the crank shaft is decreased, rotation of a rotor of the alternator is continued by its inertial force, so that the power generating efficiency can be improved.
A pulley unit A will be explained with reference to FIG. 11. A reference numeral 1 indicates a pulley. A reference numeral 2 indicates a shaft body which is concentrically disposed so as to be rotatable relative to the pulley 1. A reference numeral 3 indicates a one-way clutch which is interposed at an annular space S between the pulley 1 and the shaft body 2. Reference numerals 4 and 5 respectively indicate a deep groove ball bearing and a roller bearing that are disposed at axial direction sides of the one-way clutch 3 in the annular space S. A belt B is entrained about an outer periphery of the pulley 1, and the pulley 1 is rotationally driven by the crank shaft of the automobile engine. The shaft body 2 is fixed to the rotor of the alternator.
The one-way clutch 3 includes a plurality of rollers 31 accommodated within a cage 32. Each roller 31 is pressed by a coil spring 33 toward a wedge-shaped narrow side (i.e., a lock side) between a cam face 2a and an inner peripheral surface of the pulley 1. Deep groove bearing rings 43 and 44 are respectively formed at an inner surface of the pulley 1 and an outer surface of the shaft body 2. The deep groove ball bearing 4 includes a plurality of balls 41 and a cage 42.
The roller bearing 5 includes a plurality of rollers 51 and a cage 52. Bearing rings are directly formed at the inner surface of the pulley 1 and the outer surface of the shaft body 2. Annular seals 61 and 62 are provided so as to seal the annular space S in order to prevent leakage of lubricant. A metallic annular shield plate 7 is provided outside the annular seal 62 placed at the free end side in order to prevent muddy water from entering within the annular space S.
An operation of the pulley unit A will be described. When a rotational speed of the pulley 1 is relatively higher than that of the shaft body 2, the rollers 31 of the one-way clutch 3 roll toward the narrow side of the wedge-shaped space. Thus, the pulley unit A is moved in a locked state in which the pulley 1 is integrated with the shaft body 2 via the rollers 31 and they are rotated synchronously. When the rotational speed of the pulley 1 is relatively lower than that of the shaft body 2, the rollers 31 of the one-way clutch 3 roll toward a wide side of the wedge-shaped space. Thus, the pulley unit A is moved in a free state in which transmission of rotational power from the pulley 1 to the shaft body 2 is interrupted, and the shaft body 2 continues to rotate only by its rotational inertial force.
In accordance with such pulley unit A, under hard circumstances that water enters easily when an automobile is washed at high speed by a car washer installed at a gas station or that foreign matters such as muddy water or small stones enter easily while the automobile is traveling, it is difficult to prevent entering of such foreign matters only by the annular shield plate 7.